LCOV - code coverage report
Current view: directory - js/src/gc - Barrier.h (source / functions) Found Hit Coverage
Test: app.info Lines: 89 80 89.9 %
Date: 2012-04-07 Functions: 204 183 89.7 %

       1                 : /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
       2                 :  * vim: set ts=8 sw=4 et tw=78:
       3                 :  *
       4                 :  * ***** BEGIN LICENSE BLOCK *****
       5                 :  * Version: MPL 1.1/GPL 2.0/LGPL 2.1
       6                 :  *
       7                 :  * The contents of this file are subject to the Mozilla Public License Version
       8                 :  * 1.1 (the "License"); you may not use this file except in compliance with
       9                 :  * the License. You may obtain a copy of the License at
      10                 :  * http://www.mozilla.org/MPL/
      11                 :  *
      12                 :  * Software distributed under the License is distributed on an "AS IS" basis,
      13                 :  * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
      14                 :  * for the specific language governing rights and limitations under the
      15                 :  * License.
      16                 :  *
      17                 :  * The Original Code is SpiderMonkey global object code.
      18                 :  *
      19                 :  * The Initial Developer of the Original Code is
      20                 :  * the Mozilla Foundation.
      21                 :  * Portions created by the Initial Developer are Copyright (C) 2011
      22                 :  * the Initial Developer. All Rights Reserved.
      23                 :  *
      24                 :  * Contributor(s):
      25                 :  *
      26                 :  * Alternatively, the contents of this file may be used under the terms of
      27                 :  * either of the GNU General Public License Version 2 or later (the "GPL"),
      28                 :  * or the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
      29                 :  * in which case the provisions of the GPL or the LGPL are applicable instead
      30                 :  * of those above. If you wish to allow use of your version of this file only
      31                 :  * under the terms of either the GPL or the LGPL, and not to allow others to
      32                 :  * use your version of this file under the terms of the MPL, indicate your
      33                 :  * decision by deleting the provisions above and replace them with the notice
      34                 :  * and other provisions required by the GPL or the LGPL. If you do not delete
      35                 :  * the provisions above, a recipient may use your version of this file under
      36                 :  * the terms of any one of the MPL, the GPL or the LGPL.
      37                 :  *
      38                 :  * ***** END LICENSE BLOCK ***** */
      39                 : 
      40                 : #ifndef jsgc_barrier_h___
      41                 : #define jsgc_barrier_h___
      42                 : 
      43                 : #include "jsapi.h"
      44                 : #include "jscell.h"
      45                 : 
      46                 : #include "js/HashTable.h"
      47                 : 
      48                 : /*
      49                 :  * A write barrier is a mechanism used by incremental or generation GCs to
      50                 :  * ensure that every value that needs to be marked is marked. In general, the
      51                 :  * write barrier should be invoked whenever a write can cause the set of things
      52                 :  * traced through by the GC to change. This includes:
      53                 :  *   - writes to object properties
      54                 :  *   - writes to array slots
      55                 :  *   - writes to fields like JSObject::shape_ that we trace through
      56                 :  *   - writes to fields in private data, like JSGenerator::obj
      57                 :  *   - writes to non-markable fields like JSObject::private that point to
      58                 :  *     markable data
      59                 :  * The last category is the trickiest. Even though the private pointers does not
      60                 :  * point to a GC thing, changing the private pointer may change the set of
      61                 :  * objects that are traced by the GC. Therefore it needs a write barrier.
      62                 :  *
      63                 :  * Every barriered write should have the following form:
      64                 :  *   <pre-barrier>
      65                 :  *   obj->field = value; // do the actual write
      66                 :  *   <post-barrier>
      67                 :  * The pre-barrier is used for incremental GC and the post-barrier is for
      68                 :  * generational GC.
      69                 :  *
      70                 :  *                               PRE-BARRIER
      71                 :  *
      72                 :  * To understand the pre-barrier, let's consider how incremental GC works. The
      73                 :  * GC itself is divided into "slices". Between each slice, JS code is allowed to
      74                 :  * run. Each slice should be short so that the user doesn't notice the
      75                 :  * interruptions. In our GC, the structure of the slices is as follows:
      76                 :  *
      77                 :  * 1. ... JS work, which leads to a request to do GC ...
      78                 :  * 2. [first GC slice, which performs all root marking and possibly more marking]
      79                 :  * 3. ... more JS work is allowed to run ...
      80                 :  * 4. [GC mark slice, which runs entirely in drainMarkStack]
      81                 :  * 5. ... more JS work ...
      82                 :  * 6. [GC mark slice, which runs entirely in drainMarkStack]
      83                 :  * 7. ... more JS work ...
      84                 :  * 8. [GC marking finishes; sweeping done non-incrementally; GC is done]
      85                 :  * 9. ... JS continues uninterrupted now that GC is finishes ...
      86                 :  *
      87                 :  * Of course, there may be a different number of slices depending on how much
      88                 :  * marking is to be done.
      89                 :  *
      90                 :  * The danger inherent in this scheme is that the JS code in steps 3, 5, and 7
      91                 :  * might change the heap in a way that causes the GC to collect an object that
      92                 :  * is actually reachable. The write barrier prevents this from happening. We use
      93                 :  * a variant of incremental GC called "snapshot at the beginning." This approach
      94                 :  * guarantees the invariant that if an object is reachable in step 2, then we
      95                 :  * will mark it eventually. The name comes from the idea that we take a
      96                 :  * theoretical "snapshot" of all reachable objects in step 2; all objects in
      97                 :  * that snapshot should eventually be marked. (Note that the write barrier
      98                 :  * verifier code takes an actual snapshot.)
      99                 :  *
     100                 :  * The basic correctness invariant of a snapshot-at-the-beginning collector is
     101                 :  * that any object reachable at the end of the GC (step 9) must either:
     102                 :  *   (1) have been reachable at the beginning (step 2) and thus in the snapshot
     103                 :  *   (2) or must have been newly allocated, in steps 3, 5, or 7.
     104                 :  * To deal with case (2), any objects allocated during an incremental GC are
     105                 :  * automatically marked black.
     106                 :  *
     107                 :  * This strategy is actually somewhat conservative: if an object becomes
     108                 :  * unreachable between steps 2 and 8, it would be safe to collect it. We won't,
     109                 :  * mainly for simplicity. (Also, note that the snapshot is entirely
     110                 :  * theoretical. We don't actually do anything special in step 2 that we wouldn't
     111                 :  * do in a non-incremental GC.
     112                 :  *
     113                 :  * It's the pre-barrier's job to maintain the snapshot invariant. Consider the
     114                 :  * write "obj->field = value". Let the prior value of obj->field be
     115                 :  * value0. Since it's possible that value0 may have been what obj->field
     116                 :  * contained in step 2, when the snapshot was taken, the barrier marks
     117                 :  * value0. Note that it only does this if we're in the middle of an incremental
     118                 :  * GC. Since this is rare, the cost of the write barrier is usually just an
     119                 :  * extra branch.
     120                 :  *
     121                 :  * In practice, we implement the pre-barrier differently based on the type of
     122                 :  * value0. E.g., see JSObject::writeBarrierPre, which is used if obj->field is
     123                 :  * a JSObject*. It takes value0 as a parameter.
     124                 :  *
     125                 :  *                                POST-BARRIER
     126                 :  *
     127                 :  * These are not yet implemented. Once we get generational GC, they will allow
     128                 :  * us to keep track of pointers from non-nursery space into the nursery.
     129                 :  *
     130                 :  *                            IMPLEMENTATION DETAILS
     131                 :  *
     132                 :  * Since it would be awkward to change every write to memory into a function
     133                 :  * call, this file contains a bunch of C++ classes and templates that use
     134                 :  * operator overloading to take care of barriers automatically. In many cases,
     135                 :  * all that's necessary to make some field be barriered is to replace
     136                 :  *     Type *field;
     137                 :  * with
     138                 :  *     HeapPtr<Type> field;
     139                 :  * There are also special classes HeapValue and HeapId, which barrier js::Value
     140                 :  * and jsid, respectively.
     141                 :  *
     142                 :  * One additional note: not all object writes need to be barriered. Writes to
     143                 :  * newly allocated objects do not need a barrier as long as the GC is not
     144                 :  * allowed to run in between the allocation and the write. In these cases, we
     145                 :  * use the "obj->field.init(value)" method instead of "obj->field = value".
     146                 :  * We use the init naming idiom in many places to signify that a field is being
     147                 :  * assigned for the first time, and that no GCs have taken place between the
     148                 :  * object allocation and the assignment.
     149                 :  */
     150                 : 
     151                 : struct JSXML;
     152                 : 
     153                 : namespace js {
     154                 : 
     155                 : template<class T, typename Unioned = uintptr_t>
     156                 : class HeapPtr
     157                 : {
     158                 :     union {
     159                 :         T *value;
     160                 :         Unioned other;
     161                 :     };
     162                 : 
     163                 :   public:
     164        14105425 :     HeapPtr() : value(NULL) {}
     165        46684547 :     explicit HeapPtr(T *v) : value(v) { post(); }
     166          255833 :     explicit HeapPtr(const HeapPtr<T> &v) : value(v.value) { post(); }
     167                 : 
     168        14582531 :     ~HeapPtr() { pre(); }
     169                 : 
     170                 :     /* Use this to install a ptr into a newly allocated object. */
     171       109431186 :     void init(T *v) {
     172       109431186 :         JS_ASSERT(!IsPoisonedPtr<T>(v));
     173       109431186 :         value = v;
     174       109431186 :         post();
     175       109431186 :     }
     176                 : 
     177                 :     /* Use to set the pointer to NULL. */
     178                 :     void clear() {
     179                 :         pre();
     180                 :         value = NULL;
     181                 :     }
     182                 : 
     183                 :     /* Use this if the automatic coercion to T* isn't working. */
     184       163460501 :     T *get() const { return value; }
     185                 : 
     186                 :     /*
     187                 :      * Use these if you want to change the value without invoking the barrier.
     188                 :      * Obviously this is dangerous unless you know the barrier is not needed.
     189                 :      */
     190        34108503 :     T **unsafeGet() { return &value; }
     191         4507868 :     void unsafeSet(T *v) { value = v; }
     192                 : 
     193          292610 :     Unioned *unsafeGetUnioned() { return &other; }
     194                 : 
     195        89451153 :     HeapPtr<T, Unioned> &operator=(T *v) {
     196        89451153 :         pre();
     197        89451153 :         JS_ASSERT(!IsPoisonedPtr<T>(v));
     198        89451153 :         value = v;
     199        89451153 :         post();
     200        89451153 :         return *this;
     201                 :     }
     202                 : 
     203        10148738 :     HeapPtr<T, Unioned> &operator=(const HeapPtr<T> &v) {
     204        10148738 :         pre();
     205        10148738 :         JS_ASSERT(!IsPoisonedPtr<T>(v.value));
     206        10148738 :         value = v.value;
     207        10148738 :         post();
     208        10148738 :         return *this;
     209                 :     }
     210                 : 
     211           89745 :     T &operator*() const { return *value; }
     212       504603626 :     T *operator->() const { return value; }
     213                 : 
     214              -1 :     operator T*() const { return value; }
     215                 : 
     216                 :   private:
     217       114182422 :     void pre() { T::writeBarrierPre(value); }
     218       260479325 :     void post() { T::writeBarrierPost(value, (void *)&value); }
     219                 : 
     220                 :     /* Make this friend so it can access pre() and post(). */
     221                 :     template<class T1, class T2>
     222                 :     friend inline void
     223                 :     BarrieredSetPair(JSCompartment *comp,
     224                 :                      HeapPtr<T1> &v1, T1 *val1,
     225                 :                      HeapPtr<T2> &v2, T2 *val2);
     226                 : };
     227                 : 
     228                 : /*
     229                 :  * This is a hack for RegExpStatics::updateFromMatch. It allows us to do two
     230                 :  * barriers with only one branch to check if we're in an incremental GC.
     231                 :  */
     232                 : template<class T1, class T2>
     233                 : static inline void
     234         2253934 : BarrieredSetPair(JSCompartment *comp,
     235                 :                  HeapPtr<T1> &v1, T1 *val1,
     236                 :                  HeapPtr<T2> &v2, T2 *val2)
     237                 : {
     238         2253934 :     if (T1::needWriteBarrierPre(comp)) {
     239               0 :         v1.pre();
     240               0 :         v2.pre();
     241                 :     }
     242         2253934 :     v1.unsafeSet(val1);
     243         2253934 :     v2.unsafeSet(val2);
     244         2253934 :     v1.post();
     245         2253934 :     v2.post();
     246         2253934 : }
     247                 : 
     248                 : struct Shape;
     249                 : class BaseShape;
     250                 : namespace types { struct TypeObject; }
     251                 : 
     252                 : typedef HeapPtr<JSAtom> HeapPtrAtom;
     253                 : typedef HeapPtr<JSObject> HeapPtrObject;
     254                 : typedef HeapPtr<JSFunction> HeapPtrFunction;
     255                 : typedef HeapPtr<JSString> HeapPtrString;
     256                 : typedef HeapPtr<JSScript> HeapPtrScript;
     257                 : typedef HeapPtr<Shape> HeapPtrShape;
     258                 : typedef HeapPtr<BaseShape> HeapPtrBaseShape;
     259                 : typedef HeapPtr<types::TypeObject> HeapPtrTypeObject;
     260                 : typedef HeapPtr<JSXML> HeapPtrXML;
     261                 : 
     262                 : /* Useful for hashtables with a HeapPtr as key. */
     263                 : template<class T>
     264                 : struct HeapPtrHasher
     265                 : {
     266                 :     typedef HeapPtr<T> Key;
     267                 :     typedef T *Lookup;
     268                 : 
     269           23529 :     static HashNumber hash(Lookup obj) { return DefaultHasher<T *>::hash(obj); }
     270            8281 :     static bool match(const Key &k, Lookup l) { return k.get() == l; }
     271                 : };
     272                 : 
     273                 : /* Specialized hashing policy for HeapPtrs. */
     274                 : template <class T>
     275                 : struct DefaultHasher< HeapPtr<T> >: HeapPtrHasher<T> { };
     276                 : 
     277                 : class EncapsulatedValue
     278                 : {
     279                 :   protected:
     280                 :     Value value;
     281                 : 
     282                 :     /*
     283                 :      * Ensure that EncapsulatedValue is not constructable, except by our
     284                 :      * implementations.
     285                 :      */
     286                 :     EncapsulatedValue() MOZ_DELETE;
     287                 :     EncapsulatedValue(const EncapsulatedValue &v) MOZ_DELETE;
     288                 :     EncapsulatedValue &operator=(const Value &v) MOZ_DELETE;
     289                 :     EncapsulatedValue &operator=(const EncapsulatedValue &v) MOZ_DELETE;
     290                 : 
     291         9549209 :     EncapsulatedValue(const Value &v) : value(v) {}
     292         9619007 :     ~EncapsulatedValue() {}
     293                 : 
     294                 :   public:
     295           13500 :     const Value &get() const { return value; }
     296        10025097 :     Value *unsafeGet() { return &value; }
     297       344315222 :     operator const Value &() const { return value; }
     298                 : 
     299         4255654 :     bool isUndefined() const { return value.isUndefined(); }
     300         2369115 :     bool isNull() const { return value.isNull(); }
     301         2368980 :     bool isBoolean() const { return value.isBoolean(); }
     302               0 :     bool isTrue() const { return value.isTrue(); }
     303          108221 :     bool isFalse() const { return value.isFalse(); }
     304         2368755 :     bool isNumber() const { return value.isNumber(); }
     305               0 :     bool isInt32() const { return value.isInt32(); }
     306               0 :     bool isDouble() const { return value.isDouble(); }
     307         2378034 :     bool isString() const { return value.isString(); }
     308            1719 :     bool isObject() const { return value.isObject(); }
     309           17400 :     bool isMagic(JSWhyMagic why) const { return value.isMagic(why); }
     310                 :     bool isGCThing() const { return value.isGCThing(); }
     311          172835 :     bool isMarkable() const { return value.isMarkable(); }
     312                 : 
     313                 :     bool toBoolean() const { return value.toBoolean(); }
     314                 :     double toNumber() const { return value.toNumber(); }
     315               0 :     int32_t toInt32() const { return value.toInt32(); }
     316               0 :     double toDouble() const { return value.toDouble(); }
     317            6768 :     JSString *toString() const { return value.toString(); }
     318                 :     JSObject &toObject() const { return value.toObject(); }
     319                 :     JSObject *toObjectOrNull() const { return value.toObjectOrNull(); }
     320           85951 :     void *toGCThing() const { return value.toGCThing(); }
     321                 : 
     322               0 :     JSGCTraceKind gcKind() const { return value.gcKind(); }
     323                 : 
     324         4733145 :     uint64_t asRawBits() const { return value.asRawBits(); }
     325                 : 
     326                 : #ifdef DEBUG
     327                 :     JSWhyMagic whyMagic() const { return value.whyMagic(); }
     328                 : #endif
     329                 : 
     330                 :     static inline void writeBarrierPre(const Value &v);
     331                 :     static inline void writeBarrierPre(JSCompartment *comp, const Value &v);
     332                 : 
     333                 :   protected:
     334                 :     inline void pre();
     335                 :     inline void pre(JSCompartment *comp);
     336                 : };
     337                 : 
     338                 : class HeapValue : public EncapsulatedValue
     339                 : {
     340                 :   public:
     341                 :     explicit inline HeapValue();
     342                 :     explicit inline HeapValue(const Value &v);
     343                 :     explicit inline HeapValue(const HeapValue &v);
     344                 :     inline ~HeapValue();
     345                 : 
     346                 :     inline void init(const Value &v);
     347                 :     inline void init(JSCompartment *comp, const Value &v);
     348                 : 
     349                 :     inline HeapValue &operator=(const Value &v);
     350                 :     inline HeapValue &operator=(const HeapValue &v);
     351                 : 
     352                 :     /*
     353                 :      * This is a faster version of operator=. Normally, operator= has to
     354                 :      * determine the compartment of the value before it can decide whether to do
     355                 :      * the barrier. If you already know the compartment, it's faster to pass it
     356                 :      * in.
     357                 :      */
     358                 :     inline void set(JSCompartment *comp, const Value &v);
     359                 : 
     360                 :     static inline void writeBarrierPost(const Value &v, void *addr);
     361                 :     static inline void writeBarrierPost(JSCompartment *comp, const Value &v, void *addr);
     362                 : 
     363                 :   private:
     364                 :     inline void post();
     365                 :     inline void post(JSCompartment *comp);
     366                 : };
     367                 : 
     368                 : class HeapSlot : public EncapsulatedValue
     369                 : {
     370                 :     /*
     371                 :      * Operator= is not valid for HeapSlot because is must take the object and
     372                 :      * slot offset to provide to the post/generational barrier.
     373                 :      */
     374                 :     inline HeapSlot &operator=(const Value &v) MOZ_DELETE;
     375                 :     inline HeapSlot &operator=(const HeapValue &v) MOZ_DELETE;
     376                 :     inline HeapSlot &operator=(const HeapSlot &v) MOZ_DELETE;
     377                 : 
     378                 :   public:
     379                 :     explicit inline HeapSlot() MOZ_DELETE;
     380                 :     explicit inline HeapSlot(JSObject *obj, uint32_t slot, const Value &v);
     381                 :     explicit inline HeapSlot(JSObject *obj, uint32_t slot, const HeapSlot &v);
     382                 :     inline ~HeapSlot();
     383                 : 
     384                 :     inline void init(JSObject *owner, uint32_t slot, const Value &v);
     385                 :     inline void init(JSCompartment *comp, JSObject *owner, uint32_t slot, const Value &v);
     386                 : 
     387                 :     inline void set(JSObject *owner, uint32_t slot, const Value &v);
     388                 :     inline void set(JSCompartment *comp, JSObject *owner, uint32_t slot, const Value &v);
     389                 : 
     390                 :     static inline void writeBarrierPost(JSObject *obj, uint32_t slot);
     391                 :     static inline void writeBarrierPost(JSCompartment *comp, JSObject *obj, uint32_t slotno);
     392                 : 
     393                 :   private:
     394                 :     inline void post(JSObject *owner, uint32_t slot);
     395                 :     inline void post(JSCompartment *comp, JSObject *owner, uint32_t slot);
     396                 : };
     397                 : 
     398                 : /*
     399                 :  * NOTE: This is a placeholder for bug 619558.
     400                 :  *
     401                 :  * Run a post write barrier that encompasses multiple contiguous slots in a
     402                 :  * single step.
     403                 :  */
     404                 : static inline void
     405            1363 : SlotRangeWriteBarrierPost(JSCompartment *comp, JSObject *obj, uint32_t start, uint32_t count)
     406                 : {
     407            1363 : }
     408                 : 
     409                 : static inline const Value *
     410          762182 : Valueify(const EncapsulatedValue *array)
     411                 : {
     412                 :     JS_STATIC_ASSERT(sizeof(HeapValue) == sizeof(Value));
     413                 :     JS_STATIC_ASSERT(sizeof(HeapSlot) == sizeof(Value));
     414          762182 :     return (const Value *)array;
     415                 : }
     416                 : 
     417                 : class HeapSlotArray
     418                 : {
     419                 :     HeapSlot *array;
     420                 : 
     421                 :   public:
     422         1395337 :     HeapSlotArray(HeapSlot *array) : array(array) {}
     423                 : 
     424          761877 :     operator const Value *() const { return Valueify(array); }
     425          630957 :     operator HeapSlot *() const { return array; }
     426                 : 
     427                 :     HeapSlotArray operator +(int offset) const { return HeapSlotArray(array + offset); }
     428            2503 :     HeapSlotArray operator +(uint32_t offset) const { return HeapSlotArray(array + offset); }
     429                 : };
     430                 : 
     431                 : class HeapId
     432                 : {
     433                 :     jsid value;
     434                 : 
     435                 :   public:
     436           25698 :     explicit HeapId() : value(JSID_VOID) {}
     437                 :     explicit inline HeapId(jsid id);
     438                 : 
     439                 :     inline ~HeapId();
     440                 : 
     441                 :     inline void init(jsid id);
     442                 : 
     443                 :     inline HeapId &operator=(jsid id);
     444                 :     inline HeapId &operator=(const HeapId &v);
     445                 : 
     446       930843451 :     bool operator==(jsid id) const { return value == id; }
     447            3025 :     bool operator!=(jsid id) const { return value != id; }
     448                 : 
     449        21934579 :     jsid get() const { return value; }
     450         3672790 :     jsid *unsafeGet() { return &value; }
     451              -1 :     operator jsid() const { return value; }
     452                 : 
     453                 :   private:
     454                 :     inline void pre();
     455                 :     inline void post();
     456                 : 
     457                 :     HeapId(const HeapId &v);
     458                 : };
     459                 : 
     460                 : /*
     461                 :  * Incremental GC requires that weak pointers have read barriers. This is mostly
     462                 :  * an issue for empty shapes stored in JSCompartment. The problem happens when,
     463                 :  * during an incremental GC, some JS code stores one of the compartment's empty
     464                 :  * shapes into an object already marked black. Normally, this would not be a
     465                 :  * problem, because the empty shape would have been part of the initial snapshot
     466                 :  * when the GC started. However, since this is a weak pointer, it isn't. So we
     467                 :  * may collect the empty shape even though a live object points to it. To fix
     468                 :  * this, we mark these empty shapes black whenever they get read out.
     469                 :  */
     470                 : template<class T>
     471                 : class ReadBarriered
     472                 : {
     473                 :     T *value;
     474                 : 
     475                 :   public:
     476        32838968 :     ReadBarriered() : value(NULL) {}
     477         6086757 :     ReadBarriered(T *value) : value(value) {}
     478                 : 
     479       130475662 :     T *get() const {
     480       130475662 :         if (!value)
     481               0 :             return NULL;
     482       130475662 :         T::readBarrier(value);
     483       130475662 :         return value;
     484                 :     }
     485                 : 
     486        88286166 :     operator T*() const { return get(); }
     487                 : 
     488                 :     T &operator*() const { return *get(); }
     489        42189496 :     T *operator->() const { return get(); }
     490                 : 
     491                 :     T *unsafeGet() { return value; }
     492                 : 
     493                 :     void set(T *v) { value = v; }
     494                 : 
     495                 :     operator bool() { return !!value; }
     496                 : };
     497                 : 
     498                 : class ReadBarrieredValue
     499                 : {
     500                 :     Value value;
     501                 : 
     502                 :   public:
     503         1530574 :     ReadBarrieredValue() : value(UndefinedValue()) {}
     504           45145 :     ReadBarrieredValue(const Value &value) : value(value) {}
     505                 : 
     506                 :     inline const Value &get() const;
     507                 :     inline operator const Value &() const;
     508                 : 
     509                 :     inline JSObject &toObject() const;
     510                 : };
     511                 : 
     512                 : }
     513                 : 
     514                 : #endif /* jsgc_barrier_h___ */

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